Preheat the oven to 180'C.
Melt the butter. Place the whole eggs in a bowl and add the caster sugar and whip to the ribbon stage.
Fold the plain flour and hazelnuts into the egg mixture, followed by the melted butter.
Whisk the egg whites to soft peaks and then fold into the egg and sugar mixture. Spread on to a baking mat, transfer to the oven and bake for 7-8 minutes. Remove from the oven and leave to cool for few minutes. Turn the sponge over onto parchment paper and remove the baking mat.
Whip the double cream until thick.
Whisk together the caster sugar, egg yolks and water. Cook over a water bath and whisk often until the mixture reaches the sabayon stage.
Melt the dark chocolate over a water bath and then add the horlicks, the cocoa powder and the softened butter. Mix together gently and then fold in the sabayon followed by the whipped cream.
Spread the malted chocolate mousse on to the hazelnut sponge. Lift the sponge using the parchment paper and roll widthways and then cut into individual portions.
Dust with icing sugar and serve.
«Try making this recipe using ground almonds or pistachios instead of hazelnuts. Ideal served as a delicate canape for afternoon tea or with vanilla ice cream as a decadant dessert.»